This invention relates to a tire building machine and more particularly to an improved apparatus for turning the edges of a tire carcass ply stock over the bead cores and the stitching of the turned edges.
Tire building machines either use mechanized ply turn-up devices or variations thereon which incorporate inflatable bladders to turn the edges of the plies at the drum shoulders up and over onto the adjacent surfaces of the tire carcass of the building drum to thereby encase the spaced inextensible beads or bead cores at the drum shoulders. When building a tire carcass, the carcass plies are wrapped circumferentially around the building drum having the annular marginal ply portions of certain plies extending beyond the ends of the drum. After the carcass is built up with the proper plies, the bead rings or cores are positioned against the spaced respective annular portions of the tire carcass plies at the drum shoulders. These operations described may be done at one building station or at one of a multiple of stations. Since the annular marginal ply portions that extend over the edges of the tire building drum are not supported, it is important to provide a turn-up device that exerts an even pressure over the entire range of manipulation of the plies. The use of bladders presents several problems since the inflation of such bladders expands in accordance with the constructed reinforcement thereof whereas the marginal ply portions of the ply stock may droop or sag unevenly especially at the top and bottom portions of the building drum as compared to the side edges of the tire building drum. The present invention is directed to a mechanical turn-up device that has a wide range of movement, having the ability to engage the marginal edges of the plies in a manner to exert an even force to provide a uniform expansion and turn up followed by a turn down that maintains continual contact. This action provides a uniform tension and distribution of the ply ends thereby eliminating dimensional non-uniformity. This is particularly useful in the building of large tires where it is desirable to be able to engage the marginal edge portions of the plies on the underneath portions or inside portions as the plies extend and sag over the edges of the tire building drum. Such mechanical turn-up devices are superior over inflatable bladders since the latter have problems of structural failure of the cord fabric, misalignment of such cord fabric in their fabrication and individual cord failure that leads to uneven turn-up. Further, with the use of bladders, additional mechanisms must be used to accomplish the ply stitching whereas with the mechanical turn-up described, the stitching is performed as a follow up of the turning up of the plies whereby contact with the marginal edges of the plies is maintained to insure dimensional uniformity in the turn up and stitching.